The present invention relates to a method for detecting rollover occurrences in a motor vehicle and triggering appropriate restraining devices, the rate of rotation of the vehicle about at least one axis of rotation, in particular its longitudinal axis and/or its transverse axis, being measured with the aid of at least one rotation-rate sensor, and evaluated.
In practice, micromechanical or surface-micromechanical sensors, which function according to the tuning-fork principal or to a linear or rotational oscillation principle, are preferably used as rotation-rate sensors.
Rotation-rate sensors that function according to the rotational oscillation principle measure the Coriolis acceleration, which acts on the sensor mass due to a rotational movement of the vehicle. The following comparison between a measurement of the translational acceleration and a measurement of the Coriolis acceleration by surface-micromechanical sensors, whose sensor masses are each 2xc3x9710xe2x88x926 grams, shows that the Coriolis acceleration is a relatively small physical effect.
In the case of a translational acceleration of 3 g, which corresponds to the resolution limit of an 8-bit analog-digital converter, the force acting on the sensor mass of the acceleration sensor is approximately 60xc3x9710xe2x88x9210 Newtons. In contrast, the Coriolis force acting on the edge of the sensor mass in response to an angular acceleration of 3xc2x0/s, which also corresponds to the resolution limit of an 8-bit analog-digital converter, is approximately 4xc3x9710xe2x88x9210 Newtons. Therefore, the minimum force to be measured in a rotation-rate sensor based on the rotational-oscillation principle is approximately 15 times smaller than in the case of an acceleration sensor having the same sensor mass. Thus, such rotation-rate sensors must be designed to measure minimal forces.
Translational accelerations, which, e.g. occur in crash situations, may cause mechanical vehicle resonances, which considerably interfere with the functioning of the above-described rotation-rate sensors. In crash situations, in particular, the situation can occur in which the output signal of the rotation-rate sensor incorrectly indicates a rollover situation, and restraining devices are therefore triggered, which are not useful in the actual accident situation and may even constitute an additional injury risk to the vehicle occupants.
The present invention provides that the translational acceleration of the vehicle be considered in evaluating the rotation-rate sensor signal, in order to prevent malfunctions of the rotation-rate sensor caused by extreme translational accelerations from erroneously triggering restraining devices for a rollover event.
In the case of the present invention, it is recognized that, in a crash which may cause the rotation-rate sensor to malfunction, relatively large translational accelerations always occur, while such large translational accelerations do not occur in the case of a rollover event. In addition, it is recognized that, in the case of a crash, acceleration components always occur along all three main axes of the vehicle. In order to implement the method of the present invention, it is therefore already sufficient to measure just one of the acceleration components, i.e. to measure the translational acceleration in only one direction. Since airbag control units are usually equipped with acceleration sensors for detecting longitudinal and lateral impact, the method of the present invention may advantageously use the present hardware and evaluate the output signals of these acceleration sensors. Consequently, the present invention""s method for detecting rollover occurrences may easily be integrated into the airbag control unit, as well.
In principle, the translational acceleration measured within the scope of the method according to the present invention may be meaningfully considered in different ways, in the evaluation of the measured rate of rotation.
In one variant of the method according to the present invention, the measured translational acceleration is used to check if a crash situation exists, which could impair the functionality of the rotation-rate sensor. For this purpose, one may simply define a threshold value for the translational acceleration. Then, when the measured translational acceleration is greater than this threshold value, it is always assumed that a crash situation is present, which, in turn, is considered while evaluating the rate of rotation measured concurrently.
In a particularly advantageous variant of the method according to the present invention, the output signal of the rotation-rate sensor, i.e. the measured rate of rotation, is at least ignored for a predetermined period of time, when it is assumed, on the basis of the measured translational acceleration, that a crash situation exists, i.e. when, for example, the simultaneously measured translational acceleration of the vehicle is greater than a predetermined threshold value. Since high translational accelerations do not normally occur during rollover events, the possibility of a rollover event here is simply excluded from the beginning, regardless of the output signal of the rotation-rate sensor. In this manner, restraining devices unsuitable for the actual situation may be reliably prevented from being erroneously activated.